Hi people. I was searching on Internet about props of 3 and 4 blades for my OS .61 fx. I cant find a correctly answer about if possible put one of this two types of prop on my engine, i read that load factor is huge for use in it. i wanna now if anyone had knowledge about that or if i can use a type in specify prop of 3 or 4 blades.

Lots of people say that you don't want to go with a 3 blade prop on an engine below a 91. I am guessing that it would be the same with a 4 blade.

Most of the time people start by reducing the diameter by one inch or the pitch by one inch for each extra blade.

So for a .61 that usually runs a 12x7 you would want an 11x7 (3) blade/10x7 (4) blade... or 12x6 (3) blade/12x5 (4) blade.

This is just a starting point though, it's uncommon to run 3 blade props and almost never do you see 4 blade on such a small engine. You'll need a tachometer to verify that a 4 blade of a certain side isn't loading it down too much.

For most people in our club a .61 is a large engine

Anyways, I used to run a 3-blade 12x6 (I think it was) on my OS61FSR (I'm all electric now). As others have said, the rule of thumb is to reduce it by 1" compared with whatever 2-blade you were using.

Oh ok, i got it. But there is a online store where i can found some props?
in apc propellers had just two props but they are big.

Abenn you said that you used a 12x6 3 blades in a .61 os engine, how was it performance? more power? more RPM?

i was reading another forums and they all said that its not good put a 3blade prop in a small engine like the .61

Most of the time, multi-blade props are just used to minimize the diameter of the prop. For ground clearance reasons and to prevent blade tips from going supersonic, large planes that have a lot of power, usually use multi-blade props to get all the thrust they can from a given engine. With R/C planes, there is usually no problem with ground clearance or prop tip speed, so you are just losing some power when you run a multi-blade prop... not much, but it is measurable. It's usually best to only run them for scale reasons.

Originally Posted by KASL

Oh ok, i got it. But there is a online store where i can found some props?
in apc propellers had just two props but they are big.

Abenn you said that you used a 12x6 3 blades in a .61 os engine, how was it performance? more power? more RPM?

i was reading another forums and they all said that its not good put a 3blade prop in a small engine like the .61

It was a while back, but I think the reason was that it looked cool Maybe it was also to reduce the noise a little, by reducing the rpm -- I can't honestly remember.

I have no idea what the rpm was, but performance seemed to me to be just the same as with the 2-blader I used before. It was either a Graupner or a Master Airscrew.

12x6 or 11x7 3 blade would be fine on a .61 FX. Performance will not be better. In fact it will probably be a little worse as the more blades you have the less efficient the prop is. You probably won't notice a drop in performance though. It's subtle. The real reason we use 3 and 4 blade props is cause they look cool more that anything else.
I have a Hobby shop that stocks 3 blade Master airscrews. Feel free to check out my site. I don't deal with four blades though. 4 blades aren't big enough sellers and the spinners get expensive

i was testing some props some few days, and its true about all i read about forums, between more diameter we must reduce the pitch. So if i want use some 3 blades prop practically i must have a prop with this dimension 12x2 for the load factor in the engine. I was searching the pages that abenn give me and i saw the prop for 3blades and 4 blades are for big engines, nothing to do the hehehehehe. Someone now another prop with big diameter and low pitch? (Not apc 12,25 x 3,75 i got many of then)

A 12x2 prop wouldn't even get you past stall speed. For a .61FX, a 12x6 or 11x7 3 blade prop will work just fine. You are going to see an RPM drop, but it won't be terrible, you need a flyable pitch above all else.

Originally Posted by KASL

... I was searching the pages that abenn give me and i saw the prop for 3blades and 4 blades are for big engines, nothing to do the hehehehehe. Someone now another prop with big diameter and low pitch? (Not apc 12,25 x 3,75 i got many of then)

I didn't give any pages link in my previous posting But, I've checked and I've still got the props I actually used -- here is my 12x6 http://masterairscrew.com/12x63-blad...propeller.aspx, and here is my 11x7 http://www.graupner.de/en/products/7...8/product.aspx

Anyway, 12x6 and 11x7 3-blade props are what I actually used on my OS61, with satisfactory results. As ChillPhatCat has said, 12x2 (if anyone makes one) won't give you any flying speed on a normal glow engine.

aben, yes i know, i was searching the brands on internet and i found the pages.

To Chillphatcat, im looking for a small pitch prop, just for experimental tests.